News

Extreme Weather in parts of the world (Updated 14 February)

Parts of the world have witnessed a series of extreme weather conditions in the first six weeks of 2014, continuing a pattern that was set in December 2013.

Much of the United States of America has experienced cold waves and major winter storms, whilst California remains gripped by drought.

The United Kingdom has seen its wettest December-January period on record, with severe, widespread and prolonged flooding. A combination of strong winds, storms and high tides caused damage and flooding in other coastal areas of Europe. There has been unusually heavy snowfall in the southern Alps.

Monthly mean temperatures were extremely high from eastern Mongolia to eastern China.

Throughout this period, national meteorological and hydrological services provided forecasts and regularly-updated warnings.

Northern Hemisphere

United States of America

For much of January, the Eastern part of the United States experienced cold Arctic weather. This was counterbalanced by warmer than average temperatures in the western part of the country, so that overall, January temperatures were close to the 20th Century average, according to the U.S. National Oceanic and Atmospheric Administration. The first half of February saw major East Coast winter storms, which caused significant disruption to transport and energy networks.

The U.S. National Weather Service said that on 7 January, every state in the lower 48 states had a location that was below freezing. This has been linked to a phenomena called the Polar vortex. In the winter a deep reservoir of cold air becomes established through the atmosphere over the Arctic because of the lack of sunlight. This is usually held over high latitudes by the jet stream, a fast moving band of air 10 km up in the atmosphere which drives weather. This year, a “kink” in the jet stream allowed the reservoir of cold air to move southwards across the USA. A blocking pattern meant it was locked into place, keeping severe weather systems over much of the Eastern United States extending down to northeast Mexico.

The same high-pressure system was responsible for the intensification of the California drought, depriving the state of much-needed precipitation from winter storms, which normally account for about half the annual total precipitation. Observations collected during January indicate that the extreme lack of precipitation during October through December 2013 intensified the deficit that had developed during the previous two water years. At the end of January 2014, California was in “exceptional” drought for the first time in the 15-year-old U.S. drought monitor.

Europe

The unusually cold weather in the Eastern USA coincided with severe storms in Europe, also linked to a persistent pattern of perturbations to the jet stream.

There is a connection between the observed large scale temperature anomalies over the northern hemisphere and the so-called planetary waves. These explain the observed atmospheric disturbances in pressure and wind patterns which affected large geographical domains and resulted in opposite temperature signals and different extreme precipitation features across the Atlantic.

For the United Kingdom, in particular, the series of winter storms has been exceptional in its duration, and led to the wettest December to January period in the UK since records began. Heavy rains combined with strong winds and high waves led to widespread flooding, coastal damage and disruption.

There were more days of rain (23 days) for the UK in January than for any other month in a series dating back to 1961. A large part of southern England received twice the average rainfall for January. It was the windiest December for the UK in records back to 1969, based on the occurrence of winds in excess of 69mph.

There was prolonged and widespread flooding in many parts of England, with dozens of flood warnings (immediate action is required) and severe flood warnings (danger to life) being issued by the Environment Agency.

Between 1 and 13 February, six depressions developed over the Atlantic, impacting particularly on the UK and Ireland. A storm on 12 February caused wind gusts of 80 - 100 mph in some exposed western areas of the UK. Ireland and a number of new wave height records were reported.

Gale force winds and high tides also caused severe coastal events and some damage along the Atlantic coasts of France, Portugal and Spain during January and February. At the start of February, Venice and other parts of Italy flooded due to a combination of high tides and strong winds.

Much of Europe saw unusually mild temperatures in the first six weeks of 2014.

Germany reported the average national January temperature was 2.8 ºC above the 1961-1990 norm, according to the Deutscher Wetter Dienst. In Spain, AEMET reported a monthly average temperature of 2.0 ºC above the long term average

Much of Russia has witnessed very much above normal temperatures reaching +9°C anomalies during the week of 29 Dec-4 Jan. For example Moscow temperature Thursday averaged 2°C while January daily average temperature is -9°C.

China witnessed a dray and warm January. Average precipitation was the lowest since 1987. Many parts of China saw less precipitation by 50-80 percent than normal years, according to the China Meteorological Adminstration. The average national temperature from January 1 to 27 was minus 3.9 ºC, the second highest after 1961.

This was followed by one of the most significant multi-day heatwaves on record affected southeast Australia over the period from 13 to 18 January 2014. The major area affected by the heatwave consisted of Victoria, Tasmania (particularly the western half), southern New South Wales away from the coast, and the southern half of South Australia. Over most parts of this region, it ranked alongside the heatwaves of January-February 2009, January 1939 and (from the limited information available) January 1908 as the most significant multi-day heatwaves on record.

A number of site records were set during the summer, including:

• Melbourne had seven 40ºC days; annual average is one day

• Adelaide had 11 days of 42ºC or above; annual average is one day

• Canberra had 19 days of 35ºC or above; annual average is 5.4 days

In Argentina, the period of unusual heat which started in December 2013 continued through January and into February, especially in central and northern regions, with a number of local heat records being set, according to Argentina’s National Meteorological Service. Parts of Brazil experienced the hottest January on record. South Africa also witnessed a heatwave in mid-January.

"If you’ve been hearing that extreme cold spells disprove global warming, don’t believe it. No single weather episode can prove or disprove global climate change. Climate is the pattern of weather geographically and over seasons. A growing body of evidence suggests that the kind of extreme cold experienced by the United States is a pattern we can expect to see with increasing frequency as global warming continues."

«I believe the odds are that we can expect as a result of global warming to see more of this pattern of extreme cold in the mid latitudes and some extreme warm in the far north.»

“As yet, there is no definitive answer on the possible contribution of climate change to the recent storminess, rainfall amounts and the consequent flooding. This is in part due to the highly variable nature of UK weather and climate.

Nevertheless, recent studies have suggested an increase in the intensity of Atlantic storms that take a more southerly track, typical of this winter's extreme weather. There is also an increasing body of evidence that shows that extreme daily rainfall rates are becoming more intense, and that the rate of increase is consistent with what is expected from the fundamental physics of a warming world.

More research is urgently needed to deliver robust detection of changes in storminess and daily/hourly rain rates and this is an area of active research in the Met Office. The attribution of these changes to anthropogenic global warming requires climate models of sufficient resolution to capture storms and their associated rainfall. Such models are now becoming available and should be deployed as soon as possible to provide a solid evidence base for future investments in flood and coastal defences.”